Primary electron influx to dayside auroral oval

Abstract

Data from the Ogo 4 auroral particles experiment were analyzed to determine properties of the higher latitude region of electron precipitation in the dayside hemisphere. From 7 months of data a probability map of occurrence of this structured low‐energy precipitation was compiled. The highest probabilities are concentrated predominantly between 0500 and 1400 hours magnetic local time, and from 75° to 82½° invariant latitude. There is excellent congruity of these high probabilities of occurrence and the high probability of occurrence of discrete auroral optical emissions, which define the auroral oval in these hours. The soft energy spectrums measured and the estimated total energy influx during typical precipitation events are appropriate for producing the type of aurora observed in these hours. It is concluded that the structured low‐energy electron precipitation is the primary energy source for the dayside auroral oval.

Net field-aligned currents observed by Triad

“…The dayside electron precipitation events observed by them appear to be more related to the occurrence of discrete auroral emissions (Hoffman and Berko, 1971) than to the field-aligned currents discussed here.…”

Simultaneous particle and field observations of field-aligned currents

“…All three regions shown in Figure 9 share the feature that the lower boundary is at higher latitudes during the dayside hours than in the near-midnight hours. Hoffman (1972) has compared the quiet time (Kp less than or equal to 2+) regions of magnetic disturbance of Zmuda et al with the regions of soft (0.7 keV) electron precipitation, when Kp was less than or equal to 2 (from Hoffman and Berko, 1971a), and found excellent congruity. In fact, since electrons with energies of 0.7 keV and below are the primary electron influx to the dayside auroral regions (Hoffman and Berko, 1971a), -15 -they are the principal electrons on the dayside which are, undoubtedly, associated with the transverse magnetic disturbances seen there so frequently by the OGO-4 search coil magnetometers and by Zmuda et al (1970).…”

Distributions and characteristics of high-latitude field-aligned electron precipitation

“…For all cases where the 2.3 keV flux at 0°exceeded -2 x 107, magnetic local time and invariant latitude (A) were computed. Each of these "events" with A Ž 600 were sorted into spatial "elements", one hour wide in magnetic local time by 2½°in A, except for A 2 850, where the latitudinal extent was 50 (see for example Hoffman and Berko, 1971). …”